Reference
What the numbers mean
Every Racketlens score, angle and measure explained in plain words, with how to read it and how far to trust it.
On this page
Racketlens shows a lot of numbers. Here is each one in plain words: what it measures, how to read it and what to keep in mind.
Scores#
Score#
From 0 to 100, per kind of stroke and per session. It’s 60 % technique and 40 % consistency. The labels: solid from 75, on the way from 55 to 74, needs work below 55. It comes from one camera: read it as a trend across sessions filmed the same way, not as a grade of your tennis.
Technique#
How close your stroke is to what pro strokes have in common at three key moments (end of backswing, contact and finish). Nine things are measured at each moment: the elbow, the arm relative to the body, shoulder turn, trunk lean, both knees and the racket hand’s position in three directions. 90 is as close as a typical pro clip; half the pro clips score 90 or more.
Consistency#
How alike your strokes in the session are. 100 = identical. A consistent stroke is a stroke you can repeat under pressure.
Match with a pro#
The percentage in You look like…: how close your usual stroke is to each pro’s over the whole swing. 100 = identical. For reference, two strokes by the same pro score about 70. It’s a style hint, not a verdict.
Your stroke in numbers#
The seven numbers the scan measures on each stroke, which the history charts session by session.
| Number | What it measures | How to read it |
|---|---|---|
| Contact in front of the body | How far ahead of your hips the racket hand is at contact, in torsos | Smaller = later contact, closer to the body |
| Contact height | How high above your hips the hand is at contact, in torsos | Bigger = higher contact |
| Hitting elbow at contact | The hitting elbow’s angle at contact | 180° = a fully straight arm |
| Finish height | How high above your hips the hand ends the follow-through, in torsos | Bigger = higher finish |
| Shoulder turn | The largest turn of the shoulders relative to the hips during the backswing (on a serve, while loading) | Bigger = more coil |
| Racket-hand speed | The racket hand’s peak speed relative to your body just before contact, in torsos per second | Bigger = faster swing |
| Forward swing time | Real time from the end of the backswing (on a serve, the racket drop) to contact | Smaller = quicker swing |
The torso, the unit of measure#
A torso is the distance from your hips to your shoulders. Measuring in torsos makes the numbers independent of your height and of how far away the camera was: 1.0 torso in front of the hips means a distance equal to the length of your torso.
The key moments#
- End of backswing: when the racket gets back, just before it heads to the ball.
- Racket drop (serve): when the racket drops behind your back, just before swinging up to the ball.
- Contact: when the racket meets the ball.
- Finish: the end of the follow-through.
Stroke phases#
Step by step splits each stroke into five phases and measures 2 to 4 things in each phase’s frame. Angles are in degrees, distances in torsos, and everything is measured in the player’s own body frame (left-handers are mirrored), so it doesn’t depend on where the camera stands.
Serve
| Phase | How it’s found | What is measured |
|---|---|---|
| Toss | The tossing arm reaching up: the higher wrist, 80 % of the way from its lowest point to its highest, before the racket drops | Toss-arm elbow, toss hand above the head, toss hand in front |
| Trophy | The deepest knee bend, from just before the toss to the racket drop | Knees, trunk tilt, racket arm height, shoulder–hip coil |
| Drive | The racket drop: the racket hand as far behind the body as it gets, within 0.35 s before contact | Drop depth, leg drive, elbow |
| Contact | The moment of contact | Elbow, contact height, contact in front, trunk tilt |
| Finish | The end of the follow-through | Balance, hand across the body, trunk tilt |
Forehand, one-handed and two-handed backhand
| Phase | How it’s found | What is measured |
|---|---|---|
| Unit turn | The shoulders finishing their turn: when they’ve made 75 % of it | Shoulder–hip coil, free hand in front, front knee |
| Backswing | The racket hand as far from the contact point as it gets, within 0.6 s before the hit | Racket depth behind, knees, elbow |
| Forward swing | The racket hand’s lowest point before it swings up to the ball | Shoulder–hip coil, racket height vs. contact, elbow |
| Contact | The moment of contact | Contact in front, contact height, elbow, trunk tilt |
| Finish | The end of the follow-through | Finish height, hand across the body, balance |
A phase with ~ was found by a fallback rule or at the edge of what is looked at. It isn’t used for what to work on, nor for a session’s phase scores: in the Session tab, a phase that was ~ in every stroke shows ~ instead of a score. A measurement whose joints are hidden in the phase’s frame isn’t given. The toss is read from the arm, not the ball: the app doesn’t track the ball on a serve, but the tossing arm rises in a very recognisable way, and it’s measured the same from any camera.
How a phase is scored#
Like technique, but one phase at a time. For each measurement the app takes the range pros have in common (the 10th to 90th percentile of their strokes) and measures how far outside it you are, in typical variations. A phase’s total is compared with a typical pro’s, who is always a little outside: a median pro stroke scores 90 in every phase. Stay inside and you go up from there; the further outside, the lower. The chips use the same colours as the overall score: 75 or more, 55 to 74, under 55.
Phase scores don’t change the technique or the session score: they sit next to them. If few pro strokes of that kind have been analysed so far, you see the measurements and ranges without a score.
The ball#
| Number | What it measures |
|---|---|
| Net clearance | How high over the net tape the ball crosses, in metres (the bottom of the ball). |
| Depth | How many metres inside the baseline it lands. Smaller = deeper; negative = long. |
| Balls in | The share of balls that landed in, among those whose landing is known. |
| Ball speed | The ball’s speed off your racket, in km/h. |
- Measured or projection: whether the camera saw the flight cross the net or only its start. See Ball analysis.
- ±: the margin of error of that measurement.
Changes and noise#
- a real change: the difference between two sessions is larger than two standard errors of your normal stroke-to-stroke spread, and big enough to matter on court.
- within the noise: the difference is smaller than that. It may be the day, the camera or which strokes came up; it isn’t a change yet.
Other numbers#
- Body angles (Body tab): in degrees; 180° is a straight joint. On screen = as seen in the video; 3D est. = true estimate, independent of the camera, noisier.
- Court fit (px): how far your marks are, on average, from the fitted court. Smaller is better. See Calibrate the court.
- fps: the video’s frames per second. More fps, better slow motion and better speeds.